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-22- major fault has been encountered in the Somerset Mine. The faults which have been encountered in existing mines tend to be high angle normal faults. The steep slopes of the stream valleys and the instability of the rock strata in the North Fork Drainage Basin has contributed to numerous landslides, mud flows and rock falls. These mass wasting features have been mapped by.W.R. Junge of the Colorado Geological Survey and published as an open file report, entitled "Geologic Hazards, North Fork Gunnison River Valley, Delta and Gunnison Counties, Colorado". Geologic units exposed"in the North Fork Drainage Basin consist of Late Cretaceous•to Early Tertiary Age sedimentary strata, Tertiary Age igneous intrusives, and quaternary Age alluvial and colluvial deposits. A generalized stratigraphic column of Late Cretaceous units can be found in Figure 3. The units are described below in ascending order. The Mancos Shale is the oldest. strata exposed in the region, and is of Late Cretaceous Age. This unit is composed of over 4,000 feet of gray marine shales and minor interbedded buff sandstones. This unit is highly erodible and unstable. Erosion and oversteepening of slopes in this formation produce the numerous rock falls and landslides observed in the lower North Fork Drainage Basin (Junge, 1978). The Mesa Verde Formation is of Late Cretaceous Age. and conformably overlies the Mancos Shale. This formation consists of approximately 2,300 feet of marine and terrestrial sedimentary rocks. The Mesa Verde Formation is the coal-bearing formation in the region and is divided into four main members; the Rollins sandstone, the Lower Coal Bearing Bowie) member, the Upper Coal Bearing (Paonia) member, and the Barren Undifferentiated) member (Johnson, 1948). The Rollins sandstone member is a 120 to 200 foot thick, massive, cross-bedded, medium to fine-grained, buff to white sandstone. This sandstone is regionally extensive and resistant in outcrop and forms prominent cliffs. This member is used regionally as a marker horizon to define the top of the Mancos Shale and the bottom of the coal-bearing horizons. The Lower Coal Bearing (Bowie) member consists of 260 to 350 feet of interbedded gray shales, thin to thick lenticular beds of buff-colored, fine- to medium-grained sandstones, and coals. The top of the member is usually capped by a massive buff-colored sandstone up to 90 feet in thickness. This sandstone, however, appears not to be a single persistent bed, but is actually several thick lenticular sandstones occurring at progressively lower stratigraphic horizons from east to west. Three coal horizons exist in the Lower Coal-Bearing member, the "A" (Old King) horizon, the "B" (Somerset) horizon, and the "C" (Bear) horizon. The "A" horizon is immediately above the Rollins sandstone